1. Field of the Invention
The present invention relates generally to a system for controling a power supply for an interior room lamp located on a ceiling portion in a vehicle compartment particularly applicable to vehicles with detachable back doors such as coupe type vehicles.
2. Description of the Prior Art
A conventional lamp power supply control system whose electrical parts are installed at points on a vehicle body includes a switch associated with a back door of a vehicle.
The control system described above is exemplified by Japanese Utility Model Application Unexamined Open No. Sho 55-81433, as shown in FIGS. 1 and 2.
In FIGS. 1 and 2, numeral 1 denotes an interior room lamp mounted on the ceiling portion 2 of the vehicle body 4. Numeral 3 denotes a back door with a rear windshield mounted at the rear end of the vehicle body 4 in such a manner as to be able to pivot about suitable means mounted at the upper rear edge of the vehicle body 4. Switch elements of a switch 5 are installed at a portion of the lower edge of the back door 3 and at the opposing portion of the lower rear edge of the vehicle body 4. The switch 5 is allowed to close when the back door 3 is pivoted upward away from the lower rear edge of the vehicle body 4 and is actuated to open when the back door 3 is pivoted downward into the lock mechanism of the lower rear edge of the vehicle body 4.
In FIG. 1, symbol V denotes a vehicle battery. As shown in FIG. 1, the switch 5 is electrically inserted between the interior room lamp 1 and ground in series with the interior room lamp 1, thus forming an electric circuit. The switch 5 is so constructed as to open when the back door 3 is pivoted downward and its edge is contacted with the lower rear edge of the vehicle body 4 closed and to be closed when the back door 3 is pivoted upwardly away from the lower rear edge of the vehicle body 4 (open). Consequently, when the switch 5 is closed, the interior room lamp 1 is turned on and, on the other hand, when the switch 5 is open, the interior room lamp 1 is turned off.
The above-described conventional interior room lamp power supply control system has a problem described below.
That is to say, since the interior room lamp 1 is turned on when the back door 3 is open, the switch 5 is always closed if the back door 3 is of the detachable type and is detached from the vehicle body 4. Therefore, the electrical power in the vehicle battery V is unnecessarily consumed since the switch 5 remains closed and the interior room lamp 1 continues to be illuminated. Consequently, if the back door 3 is detached from the vehicle body for a long period of time, the battery V may discharge to such an extent that the engine of the vehicle will not start smoothly or cannot be started at all.